A previously proposed non-contact power supply device in which a serial capacitor is connected to a primary winding driven by means of an alternating current power supply, a parallel capacitor is connected to a secondary winding, and values of these capacitors are set on a basis of a mathematical equation disclosed in Patent Document 1 described below so that this transformer is substantially equivalent to an ideal transformer is known (Patent Document 1).
However, since the values of these capacitors are set with a prerequisite such that a coupling coefficient between the primary winding and the secondary winding is constant so as to achieve a high efficiency, such a problem that a power factor is reduced in a case where the coupling coefficient is varied.